The present invention relates to a position detecting apparatus for use in the fine positioning, dimension measurement, distance measurement, position information measurement of a velocity, an instrumentation, and the like and, more particularly, to a position detecting apparatus for use in measurement control which requires a resolution of the atomic order (0.1 nanometer).
Particularly, the invention is suitable for use in a high accuracy positioning apparatus for positioning or the like of a wafer in an ultradine working on the order of a nanometer such as in drawing or the like of a super LSI wafer pattern.
An encoder which can be mentioned as one of such a kind of conventional position detecting apparatuses is constructed by a reference scale having information regarding position or angle and detecting means which moves relatively with respect to the reference scale and detects information regarding the position or angle. Such an encoder is classified into several types depending on the reference scale and the detecting means. For instance, an optical type encoder, a magnetic type encoder, an electrostatic capacitive encoder, and the like have been known.
On the other hand, hitherto, in a positioning apparatus for positioning between a mask and a wafer, between a working beam head and a wafer, or the like in the ultrafine working, after the coarse positioning operations of two or three steps were executed, the fine positioning is performed. Among the position detecting apparatuses which are used in those positioning techniques, as apparatuses having a high resolution, there have been known an apparatus in which a laser beam or an electron beam is irradiated onto a positioning mark provided on the surface of a wafer and an edge of a stairway-like portion of the positioning mark is detected by the diffused lights or diffused secondary electrons and an apparatus in which a shape of a positioning mark is formed like a diffraction grating or a zone plate and a change in intensity of the reflected interference light or a positional deviation of a focused beam spot is detected.
However, in the above conventional examples, the performance (resolution) of the lattice interference optical type encoder having the highest resolution among the apparatuses which have already been put into practical use is mainly determined by a lattice pitch. An important point is how the lattice pitch is formed at fine intervals at a high accuracy and is detected at a high precision. According to the present fine working technique (for instance, in electron beam drawing or ion beam working), there is a limitation of up to ten nanometers with respect to accuracy. On the other hand, even in the detecting technique (for example, in the optical heterodyne method), there is a limitation of ten nanometers as a resolution. Therefore, when an encoder of a higher resolution is needed for a semiconductor manufacturing apparatus or the like, such a requirement cannot be satisfied.
Among the above conventional examples, in the apparatus in which the edge of the positioning mark is detected by a laser beam or an electron beam, the positioning accuracy is limited due to a focusing diameter of the laser beam or electron beam. Further, a positional detection error also easily occurs even by a defective mark or an aberration or a breakage of the mark which is caused during the working process. On the other hand, in the apparatus in which an intensity of interference light or a positional deviation of a focused beam spot is detected from the positioning mark of a diffraction grating or zone plate, the position detection accuracy is limited by a manufacturing accuracy of the mark. Therefore, even in those positioning techniques of a high resolution, there is a limitation of 0.1 micrometer as a positioning accuracy. A further higher accuracy is needed in the positioning of a wafer in the drawing or the like of a super LSI wafer pattern which is being made even finer.
On the other hand, as another conventional example, in JP-A-62-209302, there has been disclosed a parallel movement quantity detecting apparatus in which a parallel movement quantity of a stage or the like is detected by a resolution of the atomic order.
According to such a detecting apparatus, in a parallel moving apparatus of an x-y stage, an electrode needle and a monocrystal whose atom interval has already been known are respectively fixed to a fixing portion and a movable portion, the number of atoms passed is counted based on a change in potential which occurs by charges which move between them when the electrode needle passes over the atoms, and a parallel movement quantity is detected from the count value of the number of atoms and the interval between atoms.
However, even in the parallel movement quantity detecting apparatus disclosed in JP-A-62-209302, errors also occur due to a local defect of the monocrystal, errors and vibration, or a disturbance such as a temperature drift or the like. Further, since the monocrystal having a two-dimensional atom arrangement is used and the same signals are generated by the movements in the directions of x and y, a two-dimensional movement quantity is obtained by individually detecting the movement quantities in the two directions of x and y. Therefore, since parallel movement quantity drive signals in the two x and y directions are preliminarily needed, such a principle cannot be directly applied to the encoder.
An apparatus which can solve the above problems is discussed in the literature (H. Kawakatsu and T. Higuchi, SEISAN KENKYU, Vol. 40, No. 12, pages 609-611). According to such an apparatus, a probe fixed under a positioning table is two-dimensionally moved every table, opposite crystal structures are two-dimensionally scanned, a pattern matching is executed by a two-dimensional STM image obtained, and the position of the probe (namely, the position of the table) is calculated.
However, according to the structure of the apparatus, the table also must be moved for the period of time when the probe is two-dimensionally scanned to obtain a two-dimensional image, so that there is a drawback such that, for instance, in the case when work piece is put on the table, the working operation must be interrupted during the two-dimensional scanning of the probe.
As related background art by the applicant of the present invention, in EPO 304893A2 (U.S. patent application No. 235,552), there has been disclosed a recording and reproducing apparatus in which position information or the like of a pattern which is at present being detected is obtained from a signal obtained by scanning by a probe a region in which a pattern having position information or the like was formed and the probe is moved to a recording region on the basis of the position information. According to the position detection in the above apparatus, one pattern is first detected only once upon one positioning operation and the positioning is executed on the basis of the information detected. Therefore, such a position detecting method differs from that of the type in which a pattern in the same region is detected and the position is detected in a real-time manner on the basis of a change in detection information of the detected pattern from a reference pattern, which type is an object of the present invention and will be explained hereinafter.